GB783681A - A heat exchanger - Google Patents

Abstract

783,681. Heating steam boilers by hot liquids; tubular heat exchange elements. COMBUSTION ENGINEERING, Inc. Feb. 16, 1956 [March 3, 1955], No. 4854/56. Classes 64(3) and 123(2) In a boiler especially for marine use which comprises a heat exchanger wherein steam is generated by the indirect transfer of heat from a heating fluid, for example, liquid sodium, to the working medium, the heat exchanger consists of a cylindrical vessel 10 having a bottom inlet 12 for water and a top outlet 14 for water-steam mixture, the latter passing to a separator, not shown from which the steam is withdrawn and the water returns to the inlet 12' by gravity circulation. Mounted within the vessel 10 is a tube bank 16 composed of a stack of spiral, tubular coils 18 which are held in position by spacers 20 welded to upright bars 22 which are themselves welded to the vessel wall. Each coil consists of a pair of internested U-tubes such as 26, 32 positioned side-by-side and wound into a spiral coil with the return bend at the centre of the coil, the coils sloping upwardly toward the centre to allow them to be completely drained. The ends of the U-tubes extend radially through a thickened portion of the vessel wall, the inlet and outlet connections being distributed over arcs 78, 80 thereof. In order positively to prevent direct contact between the liquid sodium, for example, flowing through the coils 18 and the water passing thereover, the tubes of the coils are double-walled, as shown in Fig. 3, being' made up of a pair of concentric tubes 38, 40 having an annular passage 42 therebetween, the passage being filled with mercury or other heat-conducting fluid. The passage 42 is sealed at the tube ends by a collar 44 to which the tubes 38, 40 are welded at 46, 48 respectively. A detecting device to indicate leakage through either tube is provided consisting of an expansion chamber 50 connected with the passage 42 and having a pressure gauge 54 mounted thereon. Each end of the outer tube 40 of each U- tube is secured to the vessel wall by means of an annular connecting member 56 welded to the tube and wall and formed to accommodate limited relative movement therebetween. The liquid sodium, &c., is supplied to the inner tubes 38 from an inlet header 62 through respective expansion bend elements 64 and after passing through the tubes and expansion bend elements 70 is collected in a header 68. Baffle plates 74, 76 prevent water flow through the open centre of the coils. In a modification, the heating fluid passes over the tubes whilst the water flows therethrough.